Reflector antennas find a lot of applications such as in e.g. radio-link point-to-point and point-to-multipoint systems, radars and radio telescopes. Modern reflector antennas are often fed by different types of corrugated horn antennas. They have the advantage compared to other feed antennas that they can provide a rotationally symmetric radiation pattern with low cross polarization over a large frequency band. It is also possible with appropriate choice of dimensions to obtain a beam width that does not vary with frequency. Still, the bandwidth is normally limited to about an octave. Corrugated horns are also expensive to manufacture, in particular at low frequency where their physical size and weight become large.
Some reflector antennas are mass produced, in particular when they are small and up to about a meter in diameter, such as e.g. for application to satellite TV reception or as communication links between base stations in a mobile communication network. Even within radio astronomy there are proposals for radio telescopes that consist of several cheap mass produced antennas, such as the Allen telescope array (ATA) and the square kilometer array (SKA). ATA is already in the process of being realized in terms of mass produced large reflector antennas, and there exist similar realistic proposals for SKA. The requirement for bandwidth is incredible in both ATA and SKA, covering several octaves. In some proposed future mobile and wireless communication systems there are also requirements for antennas with large bandwidth. Such systems are often referred to as ultra wide band (UWB) systems and the broadband antenna technology as UWB antennas. As a result of the above there will be a need for new types of broadband antennas in the future, in particular antennas that can be used to feed reflectors in an efficient way.
There have recently been developed broadband feeds for reflectors that are much more broadband, lighter and cheaper to manufacture than corrugated horns. They have been obtained by locating four logperiodic antennas together in a pyramidal geometry, see Greg Engargiola “Non-planar log-periodic antenna feed for integration with a cryogenic microwave amplifier”, Proceedings of IEEE Antennas and Propagation Society international symposium, page 140-143, 2002. The beam width is constant and the reflection coefficient at the input port is low over several octaves bandwidth. However, for known log-periodic antennas of this kind the phase centre moves with frequency. This causes problems with reduced directivity due to defocusing at most frequencies. Also, the known log-periodic pyramidal feed represents a rather complex mechanical solution.